Abstract: The existence of three autochthonous crayfi sh species is confi rmed in the northwest of the Republic of Srpska: Astacus astacus, Pontastacus leptodactylus and Austropotamobius torrentium. There is a lack of  information on the European crayfi sh population status in the Republic of Srpska comparing to other European countries. Our aim is to generate the latest information on crayfi sh distribution and population status, and make it the basis for managing and preserving natural population. The present study was implemented in the period from April 2018 until September 2019. Mostly distributed crayfi sh species in the Republic of Srpska is A. torrentium registered in 12 locations at altitude ranging from 201 to 846 m in the Vrbas river basin, but it is also present in the tributary streams of the Sana river, in ecologically-like habitats, in particular in relatively clear waters with low quantity of organic substances (I and II water category). A. astacus is mainly present in the Crna river basin, forming both river and lake population (a great number thereof is present in the Balkana lake) – waters with oxygen concentration over 8 g.O2.m-3 and with BOD5 values below 0.5 g.O2.m-3. P. leptodactylus was found only in two locations: the Matura river (in Srbac) and the Vrbas river (upstream from Razboj), in the I-III category waters. The identifi ed possible threats for autochthonous crayfi sh in fresh water ecosystems of the

Republic of Srpska require urgent water management and preservation actions.

Keywords: freshwater crayfi sh, Astacidae, Republic of Srpska.